Double-boost venturi construction



1 pi. 2n, 1949 ATTURNEY Patented Sept. 20, 1949 DOUBLE-BOOST VENTURI CONSTRUCTION Francis J. Wiegand, Ridgewood, and Robert W. Scott, Packanack Lake, N. J., assignors to Wright Aeronautical Corporation, a corporation of New York Application June 8, 1945, Serial No. 598,320

Claims.

This invention relates to Venturi measuring means and is particularly directed to a Venturi measuring system capable of providing an accurate measure of the mass rate of gas flow therethrough regardless of variations in density of the gas.

The pressure differential between the entrance and throat of a Venturi tube is a measure of the magnitude of the iiuid flow through the Venturi tube. As herein after used, this pressure differential is termed the suction pressure of the Venturi tube. In the case of a gas, for a given mass flow rate through a Venturi tube, the Venturi suction pressure increases as the density of the gas decreases. By providing suitable automatically-adjustable bleeds, this suction pressure can be used for measuring the mass flow rate of the gas even though the density of the gas varies. For a given mass flow rate, a decrease in the gas density is accompanied by an increase in the gas velocity through the Venturi tube. If the gas density decreases beyond the point at which the ilow through the Venturi tube approaches the velocity of sound, the Venturi'tube no longer furnishes an accurate indication of the mass rate of gas iiow therethrough.

This phenomenon is of particular importance in aircraft engines utilizing a Venturi tube at the air entrance to the engine induction system for measuring the air ilow therethrough in order to control the fuel ow in proportion thereto. Thus, when a single Venturi tube is used on an aircraft engine for measuring the air ow, if the Venturi throat is made small enough to provide a suiciently-large suction pressure at sea level, the Venturi tube may have a critical altitude of approximately 20,000 feet at a mass rate of air flow corresponding to the sea-level rated-power of the aircraft engine. That is, at a mass rate of air iiow corresponding to the sea-level ratedpower of the engine and as an altitude of approximately 20,000 feet is approached, the velocity of the air flow through thev Venturi tube will approach the velocity of sound. However, at lower engine powers, the Venturi suction will continue to provide an accurate measure of the air flow at altitudes above 20,000 feet since the velocity of the ow through the Venturi tube will decrease with a decrease in the mass flow rate, that is with a decrease in engine power. If the single Venturi tube is made larger so that the velocity of air ow therethrough at the sealevel rated-power of the engine does not approach the velocity of sound until an altitude substantially in excess of 20,000v feet is reached, then the Venturi suction atsea'level is too small to be useful for controlling the fuel flow.

Modern aircraft engines have been and are being designed to operate at altitudes as high as 40,000 feet at rated sea level power. Accordingly, it is an object of this invention to provide a Venturi air flow measuring system which is capable of providing an accurate measure of the mass rate of air flow from sea level to an altitude as high as at least 40,000 feet for the sea-level ratedpower of the engine.

Specically, the invention comprises a double Venturi system particularly useful for measuring the air flow into an aircraft engine, which system comprises two Venturi tubes of diiierent size, the one being capable of providing an adequate suction pressure between sea level and an altitude of 20,000 feet and the other between altitudes of 20,000 feet-and 40,000 feet. In addition, barometrically and thermostatically-controlled means are arranged to adjust the suction pressure made available by said two Venturi tubes such that the Venturi system is capable of providing an accurate measurement of the mass rate of air flow from sea level to an altitude of approximately 40,000 feet and at a mass air flow rate corresponding to the sea-level rated-power of the engine.

Other objects of thisinvention will become apparent upon reading the annexed detailed description in connection withr the drawing in which:

Figure 1 is adiametric view of a fuel-air ratio portioning system embodying the invention; and

Figure 2 is a view showing the position of the automatic valve of Figure 1 at a higher altitude.

' Referring to the drawing, I0 designates the air intake conduit for the induction system of an aircraft engine havinga main Venturi tube I2 disposed therein. A double boost Venturi assembly I4 is disposed within the throat ofthe main Venturi tube I2 and comprises a rst boost Venturi tube I6 extending into and terminating substantially at the throat of the main Venturi tube AI2 and a second boost Venturi tube I8 extending into and terminating substantially at the throat ofthe first boostVenturi tube I6. As used herein, a `boost Venturi tube is a Venturi tube co-axial with and having its downstream end terminating within and substantially at the throat of another Venturi tube.

The throat or suction pressure of the rst and second boost Venturi tubes are respectively transmitted to end chambers 20 and 22 in a valve housing 24 byrconduits 2| and 23 respectively.

A compound valve 2G, piloted within an end wall of the housing and in a guide portion 21 extending thereacross, controls the communication of an intermediate valve housing chamber 28 with the end chambers 20 and 22 through valve ports 30 and 32 respectively. The suction pressure in the intermedlatechamber 28-ihat is,.the pressure differential between "the intermediate chamber 28 and the air entrance impact pressure to the Venturi system-is used to regulate the engine fuel flow in proportion to `the aai-r iow .through the conduit l by means of a suitable pressurebalancing diaphragm system 34.

As illustrated, the diaphragm-'system 34iis disposed within a housing 36 having 4a pair of Jnexible diaphragms 38 and 40 and a fixed intermediate partition 42 extending thereacrosstoidene chambers 44, 46, 48 and 50. The exible diaphragms 38 and 40 are connected together h'for joint movement by a valve stem member 52 which extends fthrough a 'lixed partition 012.

A small flexible diaphragm `154 4provides a seal between this Vfixed partition :and fthe ivalve Stem member 512. "Ihe-vellve stem :'52 extends through a valve-port opening. 56 in aisee-ond :fixed .partition 58 and in'to a-'chaniber f60. 'The .valve stemf5-2 is provided with a valve head '02 .disposed .within the 4chamberf601tor cooperation with vthe valve openingli tofprovidea fuelfow regulatingfvalve. The lvalve stem .'52 iis also :provided with small exible diaphragms at its ends 'Ito :provide sealed end chambers 1.84 and 66 therefor.

'-F-uel under pressure `'is :admitted tto :the chamberr 60 `from -a'iuel fsupplyline 68 vand rflowszthere .threug'ninto-the chamberliunder fthe control of tireiuel regulating yvalve 62 andthence through a lconduit 210 into 'a mixture-control yunit 112. 'The mixturecontrol unit 12. comprises amixture-controlnisc T4 having .a plurality vof .openings (not shown-l adapted to selectively .establish .communication between the :conduit .1'0 and iany .fone of -a fp'lurality Ao'f .restricted passagesrsuch as "L6 and 18. :From :the passage 13 andor-.passage '118, 'the fuel ilows vinto a 4conduit $0 and `iis :discharged 'therefrom into fthe air duct I0 *through a suitablefnozzle 82 disposed ibelow 8.a throttle 7valve 0.4 in the lduct l0. A `springimeans1815 5servesto urge the mixture-control disc against a at aceiinto which fthe -various passages Ht `:and 18 open and a .handle l88 is provided .for :rota-tively .adjusting the .disc 'F154 for :establishing :communication between the fuel passage and a selected restricted rpassageiii and/or T8. f'IYheiuel .conduit 80isza1so connected finto Athe ichaufnber .248 :by aconduit =90. The 'chambers 144 and i6 xoit tthe pressure-'balancing system Vare .respectively connected 'by Voonduits -92 and F94 with the :air .'-entran'ce I.opening of the Venturi system andfwith the intermediate valveihousingihamber 28.

'With fthis construtcicn, the .diaphragm .40 iis subjected to -a pressureldifferential in proportion vto the "fuel fow and, las will hereinafter appear, 'the diaphragm 38'1issuojeetedfto .a pressure dif .ferential iin proportion rtoithe .air fiiow. Accordingly, the fuel .valve B2 is=automatically :adjusted by ithe differential pressure across vvthe dia- .phragms 3'8 and Mito .vary-ithe lTiuel flow inproportion to the :airfow VThe richness :of the fuel-fair .mixture-iis determined "by `the setting of thesmix- 4ture-control-disc '114. Also, the :ohambersi and 1 6E at the ends of the-valverstem varefincommunication lwithieach other .and .withtthe "chamber 50 Vbylwayof apassages. The purpose offthislatter `rteature is to :eliminate .1an-y ipressure fdiierential .betweenzthe endsoith-e valvestem. .fAtthispoint VAIl() 4 it should be noted that the invention is not limited to the afore-described specic form of system 34 for controlling the fuel flow by a pressure differential proportional to the air iiow.

The pressure within the intermediate valve housing chamber 28 is controlled by a compound valve 2,5 which .is barcmetrically and thermostatically-controlled to compensate for variations in the air density.

To this end, the valve 26 is secured to a sealed partially-evacuated .bellows 93 whereby changes in the pressure and temperature of the air surroundingfthe bellows 4is eliective to axially adjust Ibthevalve. The bellows 88 is disposed within a y'chamber 10i! subject to the temperature and pressure 'oi lair ienteringfthe duct I0. Thus a pipe |02 may place .this :chamber in communication with the static air pressure at the entrance to the duct t8. -As Yauesult, the Valve 255 is automatically adjusted with variations inair density with altitude. 'Instead of connecting-the bellows vchamber |00 to the static air pressure atthe entrance tothe xduat 4.8, itis within the scopeof this invention -lio adonnect this chamber vto any pressure source or sources Variable with density of the `fluidow Lto be measured, as for exmple the impact pressure attireentrance tothe duct 'i0 or someother pressure associated with the Venturi system. ,Afnempression :spring `lil l maybe 'provided itc help balance :fthe pressure difierentialbetween the inside and outside of the bellows.

.Since the bellows l198 tis 'only partially evacuated, the 'bellows Vexpands and contracts lwith increase anddecrease of thefsurrounding-,air temperature. `Accordingly, an `increasein the surrounding air 4`temperature produces movement of :fthe Vvalve 2S 'in fthe same direction as 'a .decrease-1in the surrounding .-air pressure. In the `ifollovizing ,descrip- .;tion, :predetermined or so-calledstandard 1atmospheric temperature and pressure v`conditions -are assumed.

The vvalve 1.25 is vprovided with ,aglargefdiameter .portion E04 4which as illustrated in .F.igure 1 is adapted :to close 4the port 32 zbetween lthe valve housing chamber 2.2 .and the intermediate :chamber 28 at sea level. At the .same time, a reduced diameter :portion .-l-06fon the `valve :is .disposed in the port 3l] at sea level, thereby providing free communication between d'fhe end chamber 2.0 and the intermediate chamber .2.8. Therefore, at -sea leveLthe-:end chamber f22,-.which isfin communicajtion with the-.first boost .Vfenturi tube i6 through conduit 23,'.is Aclosed by thefva1ve-portionl04 While the .end 'chamber 12B ein communication with the secondiboost Venturi itube i8 ithroughconduitZflgis open to theintermediate chamber 28. .Thefpressure within this .intermediate .chamber 28 is transmitted to rthe `balacing diaphragm system chamberfl throughithe conduit ,94. v'In'.this1way, ait sea level :the diaphragm 3B is subjected to ithe suction pressure pj the second-boost Venturiitube .l' 8.

.As the .altitude increases., Ythe :suction pressure .of the second boost Venturi :tube increases for-a given f masszratcfof air iiow. -Thisgsuction-pressure is corrected to :its .sea vlevel value .by providing .a bleedvbetween theiftwofiboost Venturi tubes. .T;hus, as thealtiitudeincreases, 'the .bellows 98 expands and raises the valve z26 and, `.as :azresult, tapered valve portions |00 and :H0 respectively enter the'valve :ports30 fand 32 'to gradually close the port 30 and Iopen the Aport '32. Therefore, airis bled or ilows vfrom the lthroat of vthe -rst fboost Venturi f'tube 'I- 'through-.the iintermediate .cham- :ber-B and-the pori-,230 to fthe Ithroatoiithe second boost Venturi tube vI8 and also from the air impact pressure line through a restricted passage III' around the diaphragm 38 to the chamber 28 and thencethrough the port 30 to the throat of the second Venturi tube I8, thereby throttling the suction pressure of the second Venturi tube I8 in the chamber 28. The tapered valve portions |08 and IIO are so contoured that the available suction pressure, or pressure differential between the pressure in chamber 28 and the pressure in rconduit 92, isrsubstantially equal to the suction pressure the second boost Venturi tube I8 would have atsea level for the same mass rate of "air flow. At a predetermined altitude-for example, 20,000 feet-the valve portion |88 entirely closes the Vport 30 and a reduced diameter portion-H2 provides a maximum opening at the port 32 as `illustrated in Figure 2. .At this predetermined altitude, the suction pressure of the secondb'oost Venturi tube I8 is entirely closed to the interme- -diate chamber 28 and only the suction-pressure 'of the first boost Venturi tube IIiV is open to the intermediate chamber 28.

'^ The first boost Venturi tube I5 is designed to lhave the same suction pressure at 20,000 feet as the second boost Venturi tube I8 'has at sea level for the same mass rate of air flow. In addition, the first boost Venturi tube I6 is of such size that the velocity of flow therethrough does not approach the velocity of sound until an altitude of approximately 40,000 feet is reached for a mass air-flow rate corresponding to the sea-level ratedpower of the engine. Above 20,000 feet, thefvalve 26 continues to rise, but the port 30 remains closed and another tapered portion I I'4 on the valve gradually throttles the port opening 32. There is a small flow of air from the impact pressure line 92,through the restricted passage I II around the diaphragm 38 to the chamber 28, and thence through the port 32 to the throat of the first boost Venturi tube I6. Therefore, as the altitude increases above 20,000 feet, the valve portion I I4 gradually throttles the suction pressure in the intermediate chamber 28 to compensate for the increasing suction pressure of the main boost Venturi I6 with altitude. That is, the valveportion I I4. is so contoured that above 20,000 feet, the valve automatically corrects the suction pressure in the chamber 28 to the magnitude of suction pressure the first boost Venturi tube I6 would have at 20,000 feet for the same mass rate of air flow.

With this construction, between sea level and 20,000 feet, the air pressure differential made available for regulating the fuel flow is equal to the suction pressure the second boost Venturi tube I8 would have at sea level for the same mass rate of airflow. Between 20,000 and 40,000 feet, the air pressure differential made available for regulating the fuel flow is equal to the suction pressure the first boost Venturi tube I6 would have at 20,000 feet for the same mass rate of air flow, which value corresponds to the suction pressure of the second boost Venturi tube I8 at sea level for the same mass flow rate. Accordingly, the double boost Venturi system provides accurate suction pressure measurement of the mass rate of air flow into an engine at high or low altitudes and at high or low mass air flow rates.

At this point, it should be noted that the invention obviously is not limited to the aforementioned specific critical altitudes-namely, 20,000 and 40,000 feet for the two boost Venturi tubes. Also, the main Venturi tube I2 only increases the suction pressures made available by the boost Venturi tubes I6 and I8. Accordingly, if smaller suction pressures can be used to con trol the fuel valve 62, the main Venturi tube I2 could be dispensed with, in which Icase the Venturi tube I6 may be increased in diameter to that of the pipe I0 and the boost Venturi tube I8 correspondingly increased in diameter.

While we have described our invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding our invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. We aim in the appended claims to cover all such modifications.

We claim as our invention:

1. Mechanism for controlling the fuel-air ratio of the'combusticn mixture for an engine, said mechanism comprising a first Venturi tube in the air flow path, a second Venturi tube disposed as a boost Venturi tube in relation to said first Venturi tube, a chamber, means providing a first passage to establish communication between said chamber and the throat of said first Venturi tube, means providing a second passage to establish communication between said chamber and the throat of said second Venturi tube,imeans having a plurality of valve portions cooperable with and movable relative to both said passages so as to vary the extent to which both said passages are open or closed, barometric means for mcvingfsaid valve portions so that at a low altitude said valve portions are eiective to close said first passage and open said second passage and upon an increase in altitude to a predetermined value said valve portions are effective to closesaid second passage and open said first passage and upon further increases in altitude said valve portions maintain said second passage closed and effect closing adjustments of said first passage, and means responsive to changes in pressure in said chamber for regulating the fuel vfow. Y

' 2. Mechanism forcontrolling the fuel-airy ratio of the combustion mixture for an engine, said vmechanism comprising a first Venturi tube in AVenturi tube, means'providing a second passage to establish communication between said chamber and the throat of said second Venturi tube, means having a plurality of valve portions cooperable with and movable relative to both said passages so as to vary the extent to which both said passages are open or closed, barometric means for moving said valve portions so that at a low altitude said valve portions are effective to close said first passage and open said second passage and upon an increase in altitude to a predetermined value said valve portions are effective to close said second passage and open said first passage and upon further increases in altitude said valve portions maintain said second passage closed and effect closing adjustments of said first passage, means responsive to the pressure differential between a pressure in the air flow path and the pressure in said chamber for regulating the fuel flow, and a restricted bypass passage for said pressure differential around said responsive means.

3. Mechanism for controlling the fuel-air ratio fl of the combustion lmixture for an engine: said mechanism comprising means movable in response to changes in the iiuid jpressure acting thereon for controlling the fuel fici/v a rst Venturi tube in the air ow Vpath; a second Ven- 4 turi tube disposed as a boost Venturi tube in relation to said rst Venturi tube; lmeans providing a -rst passage to establish communication between throat oi said first Venturi 4tube .and said fluid pressure responsive means; means .providing a second passage lto establish communication between the throat o f said second Venturi tube and 4said iiuid pressure `responsive means; means having a plurality of Valve por.-

tions cooperable with and movable relative to both said passages for controlling the extent to which both said passages vare open or closed and b aronietric means Vfor controllingsaid valve portions so that at a lov.l altitude said first passage is closed and said second passage is open, said valve portions aso being arranged so that as said ,altitude increases, from said W altitude, said irst and second passages are progressively opened and Vclosed respectively and, as said altitude increases above a predetermined high value, said second passage remains closed and said lfirst passage is progressively closed.

4. Mechanism for controlling the fuel-airratio of the vcombustion mixture for an engine: said mechanism comprising a firs-t Venturi tube in the air flow path; Va Asecond Venturi 4tube disposed as va boost Venturi tube in relation to said iirst Venturi tube; a chamber; means providing a rst vpassage having oneend adapted to communicate vwith said chamber and having its other endl-opening into the throat oi said first Venturi tube.;

`means providing a second passage having oneend :adapted to communicate with said chamber and having its other end opening -into the throat of said second Venturi tube; a first-valve movable vto control said rst passage; a second valve v,move

`able to control 4said second passage; barometric means for automatically controlling said Iiirst and second valves so that at alow altitude said yiirst valve -is at a minimum open position and ,said second valve is at Va maximum open position and as said altitude increases to a predetermined value said iirst 'valve moves -to its maximum open position andsaid second valve :moves to its minimum open position and at still higher altitudes said second valve remains'at a minimum open position and said rst valve moves in 4a and Ymeans responsive to changes :in pressure fin vsaid `chamber @to regulate theaiuel iiow.

5....Meohanism for controlling vthe fuel-,airratio of Ythe combustion mixture for an engine: said meehanisrnfcomprising a rst Venturi tube inthe airowpath; a second Venturi tube ,disposedas .ze `lli-most Venturi tube lin relation to said first Venturitube; a chamber; ,means providing f-a first ,passage having one lend adapted -tocommunicate iwithsaidfchamber and having its other end open.- ing into the throat `oi said rst Venturi tube; means providing a-second passage having one end adapted t 0 communicate with said chamber and .having its other end opening into the throat of :said second Venturi tube; a first valve movable ite-control said rst passage; a second valve mov,- ftable A.to control Vsaid second passage; barometrie fmeans for lautomatically controlling said rst and :semina-valves so vthat at `a, low altitude said irst valve fis at ga minimum .open position and said second valve is at a maximum open position and as said altitude increases to a predetermined value said rst valve movesto its maximum open vposition and said second valve moves to its vminimum open position and at still higher :altittudes said second valve remains at a minimum open position and said rst valve moves sa Iclosing direction; means responsive to the pres- :sure ydifferential between air pressurein saidyiiow path Yand lthe fluid pressure in said chamber lfor :regulating the fuel flow; and means providing a restricted lov-pass passage :for said pressure -:differential around said responsive means.

` FRANCIS J. 'WIEGAND ROBERT W. SCOTT.

REFERENCES CTED "The following references are of record in the l'e of this patent:

UNITED STATES 'PATENTS Number Name Date 2,216,677 lSchuttler Oct. 1, 1940 2,361,227 Mock Oct. 24, 1944 2,391,755 Twyman Dec. 2 5, 1945 2,396,031 Udale et al. Mar. 5, 19,46 2,399,079 Udale Apr. 23, 1946 2,411,287 Mock Nov. 19, 1946 FOREIGN PATENTS Number Country Date 135,557 Great Britain Dec. 4, 191,9 561,017 Great Britain May 2, 1944 

